This invention relates in general to an improved method of and apparatus for clarifying liquids and, in particular, to a filtration system especially adapted for use in processing edible oils. More specifically, but without restriction to the particular use which is shown and described, this invention relates to a vertical leaf filtration system which automatically cleans the filter elements upon accumulation of a predetermined amount of materials from the influent without opening the filter chamber and maintains filter cake integrity during precoating and drying of the expended filter cake and accumulated materials.
While the instant invention has many applications, it is especially useful in process filtration of edible oils and for convenience of illustration will be described with reference to its use in edible oils processing. As is well known, seeds such as soybeans, cotton seeds, peanuts, and others, as well as animal fats such as tallow, lard, and others, contain sufficient quantities of vegetable oils and animal fats to justify commercial recovery and processing for edible and other industrial uses. In such processing, the oil or fat is removed from the oil bearing material by extraction with solvents such as hexane, alcohol, acetone, furfural, or other such suitable solvent, by such equipment as an expeller, press, or a combination thereof. The oil, or miscella, thereby removed is clarified by passing through filters which separate the liquid from the solid for the recovery and processing of the oil.
In some applications it is desirable to degum the crude oil to remove the water and soluable phosphatides, gums, etc. In such applications the crude oil is treated with water and phosphoric acid, or any other suitable reagent, to precipate the gums. While these precipated gums are presently removed by centrifuge, with a suitable filtration system the gum removal would be more complete. The degummed oil is then treated for the reduction of the free fatty acids. The more complete the removal of the gum, phosphatides, etc., the better the recovery of the free fatty acids reduced by physical refining. However, if the gums are not completely removed, or if there is no degumming, the gums in the free fatty acids must be removed by caustic neutralization of the free fatty acids with a slight caustic excess. Such caustic neutralization hydrates the gum and converts the free fatty acids to soaps which are subsequently removed by a centrifuge. The refined, or neutralized and degummed oil (which desirably has a free fatty acid content below 0.05% ) is treated with bleaching agents (earth) under heat and vacuum to reduce the color. These bleaching agents are then removed by filtration.
If it is desirable to lower the melting point of the oil, the oil is hydrogenated by bubbling hydrogen gas through the oil in the presence of a catalyst. While nickel has been found to be a suitable catalyst, it is difficult to remove the nickel from the oil requiring some filter aid material to be added to the material to facilitate catalyst removal. This nickel catalyst and filter aid is subsequently removed by filtration and the oil post bleached--a process referred to as re-bleaching after hydrogenation. The bleaching agent, generally a neutral earth, is then removed from the oil by filtration along with any residual catalyst.
The edible oil may then be further processed, such as by winterizing and/or deodorizing, which require filtration to insure the removal of all the solids from the oil. After deodorizing a final processing step, filling, is effected wherein the liquid ingredients are filtered to remove foreign materials.
In the various filtration steps required in edible oil processing, the filtration systems heretofore employed were such that the filter apparatus had to be disassembled whenever the filter elements required cleaning for removal of the accumulated sludge or accumulant bearing expended filter cake. Such disassembly released vapors, which were sometimes toxic, into the atmosphere in the presence of the system operators and others creating an undesirable and sometimes hazardous working environment. The filter elements were then removed from the filter chamber and the filter septum scraped by hand which frequently resulted in damage to the filter elements by puncturing or distorting the filter cloth wire mesh septum. Once cleaning had been accomplished, the filter elements had to be reassembled within the filter chamber and frequently were not properly sealed. Such improper sealing in combination with the puncturing or distorting of the filter septum frequently resulted in influent contaminating the filtrate. In an attempt to minimize this problem, fiber filter aids were used with the precoat filter aids to create a proper seal and to attempt to maintain septum integrity. The use of such fiber filter aids is very costly and the necessity to effect such seals results in a very xpensive and inefficient filtration system.